As an example of a magnetic recording medium, there has been proposed a patterned medium (PM), wherein a magnetic layer is physically divided into plural areas by patterning the magnetic layer to increase the recording density. Examples of the PM manufacturing method include a method, wherein a magnetic layer is formed on a substrate, followed by patterning the magnetic layer; and a method, wherein a substrate of a magnetic recording medium is patterned, followed by forming a magnetic layer on the patterned substrate to thereby form the magnetic layer having a pattern corresponding to the pattern of the substrate.
The method, wherein a magnetic layer is formed on a substrate, followed by patterning the magnetic layer, has a problem that the magnetic layer may be deteriorated by e.g. etching at the time of patterning. In order to solve the problem, there has been proposed an idea of forming a protective layer for protecting the magnetic layer on the magnetic layer before patterning is performed. For instance, patent literature 1 discloses a recording medium manufacturing method including: forming a recording material layer (magnetic layer) on a medium substrate; forming a resist layer (protective layer) on the recording material layer; pressing an imprint master (mold) against the resist layer to transfer concave and convex configurations on a surface of the imprint master onto the resist layer; depositing particles of masking material in concaves formed in the resist layer; and patterning the resist layer and the recording material layer, using the particles of masking material as a mask to form a patterned recording layer. However, adding a step of forming a protective layer on a magnetic layer makes the manufacturing process cumbersome and makes it difficult to achieve high throughput. Dry-etching is used in the above etching step. Dry-etching is normally performed under a vacuum condition. Therefore, in performing etching, the interior of the apparatus is required to be brought to a vacuum state, which hinders achieving high throughput.
For instance, as an example of a method for patterning a substrate of a magnetic recording medium, patent literature 2 discloses a pattern forming method including: coating, on a substrate, a diblock copolymer film containing two polymeric components having different etching resistances; subjecting the diblock copolymer film to phase-separation to form one of the polymeric components into a cylinder or a lamella; applying an imprint on the diblock copolymer film, using an imprint mold having a line pattern; forming first concaves intersecting with the length direction of the cylinder or the lamella; forming second concaves by removing the polymeric component in the form of the cylinder or the lamella; embedding a silicon-containing resist into the first and the second concaves; etching the diblock copolymer film, using the silicon-containing resist as a masking material, followed by etching the substrate. In the above technology, a substrate is etched to form a pattern, using a silicon-containing resist as a masking material. The above technology may cause a drawback called “micro loading effect” that the etching rate is changed depending on the degree of density of the pattern. Normally, there exist, as a pattern for PM, a pattern for use in data recording, and a servo pattern for use in tracking data; and the configurations of the respective patterns differ from each other. In other words, since the micro loading effect occurs in the above technology, it has been difficult to uniformly process all the patterns having different configurations.
Further, in performing etching, the following drawback may occur, in the case where e.g. a general reactive ion etching (RIE) is used as dry-etching. RIE is a method for etching a surface of an object to be processed by colliding radicals or ions generated by plasma discharge against the object to be processed. The distance between adjacent convexes of a pattern for PM is normally as small as several ten nanometers, and the distance is required to be further reduced in order to enhance the recording density. In the case where a pattern having such a small convex-to-convex distance is formed, the size of the openings of a mask to be used in etching becomes extremely small. With such excessively small openings of the mask, it has been difficult to perform etching, because radicals or ions are less likely to be intruded into the mask. Further, since the above method also uses dry-etching, the above method has not been suitable for achieving high throughput.
In view of the above, there has been proposed a method for forming a pattern by a nano imprint method, as a method for solving the above drawbacks. As a method for forming a pattern by a nano imprint method, for instance, patent literature 3 discloses a method for manufacturing a magnetic recording medium including: a step of forming a member to be transferred (imprint material) on a flat substrate or on a mold having a concave and convex structure; a step of pressingly contacting the mold against the member to be transferred; a step of transferring the concave and convex structure of the mold onto the member to be transferred; a step of removing the mold from the member to be transferred; and a step of depositing and forming a magnetic recording layer on the member to be transferred and having a structure corresponding to the concave and convex structure of the mold. Specifically, the nano imprint method is a method including: pressing a mold having concave and convex configurations on a surface thereof against an imprint material coated on a substrate base member to transfer the concave and convex configurations onto the imprint material, and solidifying the imprint material, followed by removing the mold to thereby acquire a substrate having concave and convex configurations on the surface thereof.
Use of the nano imprint method as disclosed in patent literature 3 enables to realize high throughput, because the number of steps is small as compared with a case of performing etching, for instance, manufacturing can be performed under an atmospheric condition, which does not require a step of bringing the interior of the apparatus to a vacuum state.
However, in the nano imprint method as described above, it has been difficult to satisfy both of the requirements on chargeability of an imprint material into a mold and releasability of the mold, after concave and convex configurations are transferred to the imprint material.
Specifically, if the nano imprint method is performed without applying a specific process to the mold, a releasability-related problem may occur, namely, the imprint material is likely to remain in e.g. the concave and convex configurations of the mold in releasing the mold from the imprint material after the concave and convex configurations are transferred. If a substrate is fabricated in a state that the imprint material remains in the mold, it is impossible or difficult to obtain intended concave and convex configurations on the fabricated substrate. This requires manufacturing a mold again, which may lower the throughput, and increase the manufacturing cost.
There is proposed an idea of coating e.g. a fluorine-based parting agent on a mold in advance in order to solve the releasability-related problem. Since the parting agent repels the imprint material, the imprint material is less likely to remain in the mold at the time of releasing the mold from the imprint material after concave and convex configurations are transferred. However, since the fluorine-based parting agent is coated on the mold in advance, a chargeability-related problem may occur, namely, the imprint material is likely to be repelled by the parting agent even if the mold is pressed against the imprint material, and the imprint material may not be sufficiently charged into the concaves of the mold.
As described above, in the conventional nano imprint method, it has been difficult to satisfy both of the requirements on chargeability of an imprint material, and releasability of a mold.